The present invention relates to an embossed plastic web in which, before a plastic web carried continuously is wound into a roll, embossing rollers having embossing uneven portions formed in their outer circumferences are pressed against side edge portions of the plastic web to form embossed surface portions of predetermined width respectively in the side edge portions of the plastic web along the carrying direction of the plastic web; and relates to a method and apparatus for performing embossing on such a plastic web.
As disclosed in Japanese Patent Unexamined Publication No. Sho-63-74850, when a plastic web (such as a photographic film support, a wrapping film, or the like) carried continuously is wound into a roll, embossing is performed on side edge portions of the plastic web to form uneven portions along the direction of carriage. This is to prevent widthwise displacement at the time of winding so as to improve the roll winding property, to ensure a space between plastic web overlaid by winding, and to improve the dealing property of the above-mentioned plastic web in the stage of working thereafter.
FIG. 7 shows a conventional example of an embossing finish apparatus for giving unevenness onto the opposite side edge portions of a thermoplastic resin film web carried continuously, when the film web is wound into a roll. In FIG. 7, the reference number 1 represents a winding shaft; 2, a take-up roll; 3, a film web carried continuously to be wound onto the take-up roll 2; 4, embossing rollers for performing unevenness onto the film web 3; 5, rubber rollers for holding the film web 3 in cooperation with the embossing rollers 4; and 6, embossed surface portions which are uneven portions formed on the film web 3 by the urging of the embossing roller 4 against the film web 3. The arrow A in the drawing shows the direction of carriage of the film web 3.
The embossing rollers 4 and the rubber rollers 5 are rotatably supported and positioned in such a manner that the outer circumferential surfaces of the embossing rollers 4 are urged against the film web 3 with predetermined pressing force so that the embossing rollers 4 rotate following the carriage of the film web 3.
A plurality of projection arrays 8 are formed on the outer circumferential surface of each of the embossing rollers 4 in such a manner that each of the projection arrays 8 is constituted by a plurality of projections formed at a constant pitch in the widthwise direction of the film web 3 and that the projection arrays 8 are formed equidistantly in the circumferential direction of the roller 4. (In most cases, each of the projections constituting the projection arrays 8 is shaped so as to be a frustum of a circular cone (circular cone with its head cut) as shown in FIG. 3. The shape is, however, not limited to this, but various shapes have been investigated.)
With the above configuration, the embossed surface portions 6 having the same outer circumferential shapes as those of the embossing rollers 4 are formed respectively on the opposite side edge portions of the film web 3 which has passed the embossing rollers 4.
In order to prevent the overlaid surface portions of the wound film web 3 on the take-up roll 2 from rubbing each other, it is preferable that uneven portions 9 of the embossed surface portions 6 formed by the embossing rollers 4, on the overlaid surface portions of the film web, are shifted from each other so that the uneven portions 9 may act as spacers to ensure a space S between the overlaid surface portions of the wound film web 3 as shown in FIG. 8.
Generally, however, the outer diameter of each of the embossing rollers 4 is smaller than the winding diameter of the film web 3 on the take-up roll 2. Accordingly, while the film web 3 is wound so that the surface portions of the film are overlaid on each other, the embossed surface portions 6 with the same pitch are repeated in the same circumferential surface, so that the uneven portions 9 of the embossed surfaces 6 of the film web 3 overlaid upon each other coincide with each other. In a conventional apparatus, in such a case, as shown in FIG. 9, the uneven portions 9 of the overlaid surfaces of the film web 3 fit in/on each other over a predetermined length in the circumferential direction so that the proper space S cannot be ensured. Accordingly, there has been a problem that rubbing-together between the overlaid surface portions of the film causes injuries or electric charges which may cause a trouble in secondary working, cause adhesion or wrinkles between overlaid portions of the film web 3, cause buckling of the uneven portions 9 fit in/on each other, and so on.
The above-mentioned Japanese Patent Unexamined Publication No. Sho-63-74850 teaches to make the array direction of the uneven portions 9 oblique relative to the film carriage direction. Since the same pitch is repeated in the circumferential direction even if the array direction is oblique, the uneven portions 9 fit in/on each other so that there is the same problem as that mentioned above.